<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>border</title>
    <style>
        .triangle {
            width: 0;
            height: 0;
            border: 50px solid;
            /* border 的构成原理，四个参数 上 右 下 左 */
            border-color: red green blue yellow;
        }
    </style>
</head>
<body>
    <div class="triangle"></div>
</body>
</html>